Sliding key and continuously variable transmission

ABSTRACT

A sliding key slidable in an axial direction of a rotary shaft and engaging a sliding cylinder such that the sliding key follows a rotation of the sliding cylinder. The sliding key is a molded product of a metal-molded part and a resinous part. The sliding key does not malfunction or fail when it is used in an environment of a high temperature and a high load.

TECHNICAL FIELD

The present invention relates to a sliding key that consists of acomposite molded product made of a metal-molded part and a resinous partand can be suitably used in a severe environmental condition of a hightemperature and no lubrication and a continuously variable transmissionusing the sliding key.

BACKGROUND ART

As a construction of a continuously variable transmission using asliding key, the pulley construction is known in which a stationary keyrotating with a rotary shaft and a movable pulley having a slidingcylinder are engaged each other through the sliding key (Japanese PatentApplication Laid-Open No. 8-219258).

With reference to FIGS. 4 and 5, the conventional pulley construction ofthe continuously variable transmission is described below. FIG. 4 is ahalf-sectional view showing the pulley construction in the axialdirection of the rotary shaft. FIG. 5 is a perspective view showing amain portion of the rotary shaft.

A rotary shaft 4 that is driven by an engine not shown is supported on abody 6 of the continuously variable transmission by bearings 5 a, 5 b. Astationary pulley 7 is formed integrally with the rotary shaft 4 suchthat the stationary pulley 7 projects outward from the rotary shaft 4.Grooves 4 b are formed concavely into the periphery of a stepped portion4 a formed on the periphery of the rotary shaft 4 such that the grooves4 b are long in the longitudinal direction of the stepped portion 4 aand spaced at regular intervals in the circumferential directionthereof. A sliding key 1 is fitted into the groove 4 b and engages amovable pulley 8 having a slidable cylindrical portion 8 a, such thatthe movable pulley 8 operates in contact with the stationary pulley 7 orseparably therefrom. The sliding key 1 that is fitted into the groove 4b is required mainly to have a rotation-stopping function or apower-transmitting function. The sliding key 1 is also required as anadditional function to have a reciprocating function in the axialdirection of the rotary shaft 4. Referring to FIG. 4, reference numeral9 denotes a V-belt spanned between the stationary pulley 7 and themovable pulley 8.

The sliding key 1 is hitherto formed of metal or a material having a lowfriction coefficient. As the material having a low friction coefficient,a mixture of polyimide resin, polytetrafluoroethylene resin, andgraphite or a mixture of polyetherether ketone resin, carbon fiber, andpolytetrafluoroethylene resin is used.

However, in the case where the groove into which the sliding key isfitted is made of metal, sliding contact occurs between the metal of thesliding key and that of the groove. Thus, when the sliding key is usedin an environment of a high temperature and a high load, the frictionresistance of the sliding key becomes large owing to friction-causedseizing of the metals or corrosion. As a result, the sliding keymalfunctions or fails. Using a ball spline construction instead of metalleads to a complicated construction and a high cost.

A conventional sliding key made of a resinous material having a lowfriction coefficient melts, deforms or has a high friction resistance,when it is used in an environment of a high temperature and a high load.Consequently, it is destroyed in a short period of time.

The present invention has been made to overcome the problem. Thus, it isan object of the present invention to provide a sliding key that doesnot malfunction or fail when it is used in an environment of a hightemperature and a high load and also provide a continuously variabletransmission using the sliding key.

DISCLOSURE OF THE INVENTION

The sliding key of the present invention that engages a sliding cylinderwith sliding in an axial direction and follows a rotation of a rotaryshaft comprises a composite molded product made of a metal-molded partand a resinous part.

The resinous part forming an integral molded product consists of aninjection-moldable resinous composition.

The continuously variable transmission of the present invention includesa stationary pulley rotating with a rotary shaft having a plurality ofgrooves formed on a peripheral surface thereof at appropriate intervalsin a circumferential direction thereof and having a sliding key fittedinto each of the grooves; and a movable pulley having a sliding cylinderhaving a plurality of grooves each of which has a width to receive thesliding key and extends axially on an inner peripheral surface thereofsuch that the grooves are located at appropriate intervals incorrespondence to the grooves formed on the peripheral surface of therotary shaft. The sliding key is the sliding key of the presentinvention.

The sliding key of the present invention is a composite integral moldedproduct of the metal-molded part and the resinous part. Thus, when thesliding key is used in an environment of a high temperature and a highload, it does not malfunction or fail. Further, because the resinouspart is made of the injection-moldable resinous composition, it is easyto form the sliding key having a complicated configuration orconstruction. Therefore, the sliding key of the present invention issmaller, lighter, and lower in cost than a ball spline conventionallyused.

Because the continuously variable transmission of the present inventionuses the sliding key, it is allowed to have a simple construction and asmooth operational performance in an unlubricated atmosphere.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view entirely showing an example of a slidingkey.

FIG. 1B is a perspective view showing a metal-molded part.

FIG. 2A is a perspective view entirely showing another example of asliding key.

FIG. 2B is a perspective view showing another metal-molded part.

FIG. 3A shows a rotary shaft into which a sliding key is fitted.

FIG. 3B is a sectional view showing the rotary shaft in its diametricaldirection.

FIG. 4 is a half-sectional view showing the construction of a pulley inthe axial direction of the rotary shaft.

FIG. 5 is an exploded perspective view showing a main portion of therotary shaft.

FIG. 6 shows a repeating shearing fatigue testing machine.

FIG. 7 shows a friction-testing machine.

BEST MODE FOR CARRYING OUT THE INVENTION

The sliding key of the present invention will be described below withreference to FIGS. 1A through 2B. FIGS. 1A and 2A are perspective viewseach showing a sliding key entirely. FIGS. 1B and 2B are perspectiveviews each showing a metal-molded part entirely.

A sliding key 1 consists of a metal-molded part 2 and a resinous part 3.The resinous part 3 is formed integrally with the metal-molded part 2,using integral molding.

The sliding key 1 is so configured that it can be fitted into a groove 4b formed on the periphery of a stepped portion 4 a of a rotary shaft 4shown in FIG. 3 that will be described later and is not dislocatedagainst a load axially applied thereto. Preferably, the sliding key 1 isalso so configured that a part thereof being fitted into the groove 4 bis formed of a metal-molded part 2 and that a part thereof sliding on agroove formed on the inner periphery of a slidable cylindrical portion 8a is formed of a resinous part 3. By forming the fit-in part of themetal-molded part 2, the fit-in force of the sliding key 1 can beimproved. By forming the sliding part of the resinous part 3, theperformance of the sliding contact between the slidable cylindricalportion 8 a and the rotary shaft 4 can be improved.

As the metal-molded part 2, it can be used machined products, forgings,lost wax products, sintered metal products, and metal-injected products.Of these products, the lost wax products are more favorable than otherproducts because the lost wax products are reliable in strength andinexpensive. To prevent the surface of the metal-molded part 2 frombeing corroded, it is preferable to plate on its surface.

It is preferable that the metal-molded part 2 is so configured that theresinous part 3 and the metal-molded part 2 are not separable from eachother during operation of a continuously variable transmission.Specifically, as shown in FIGS. 1B and 2B, a groove 2 a and athrough-hole 2 b are formed on the metal-molded part 2. Owing to theformation of the groove 2 a and the through-hole 2 b, in performingintegral molding, the resinous part 3 is filled into the groove 2 a andthe through-hole 2 b to form a composite product of the resinouscomposition and the metal. Therefore, the sliding key 1 of the presentinvention can be formed as a rigid integral molded product without usingan adhesive agent. A corner 11 of the metal-molded part 2 has a radiusto flow resin easily.

As the resinous composition forming the resinous part 3, it is possibleto use resinous compositions that can be molded integrally with themetal-molded part 2. As the molding method, injection molding,compression molding, and transfer molding can be used. Aninjection-moldable resinous composition is preferable because it can beeasily processed into the resinous part 3 even though the metal-moldedpart 2 has a complicated configuration.

As the injection-moldable resinous component, it is possible to usethermoplastic polyimide resin, polyetherketones such aspolyetheretherketone resin and polyetherketone resin, polyacetal resin,polyamide resin, polyethylene resin, polyamide-imide resin,polyethernitrile resin, aromatic polyester resin, and polyphenylenesulfide resin. These resins can be used singly or as a polymer alloy ora polymer blend consisting of two or more of the resins.

Of these resins, resin containing both the thermoplastic polyimide resinand the polyetherketones as its main component is preferable because theresins allow formation of the sliding key having a high degree ofmechanical strength and sliding performance.

Regarding the thermoplastic polyimide resin, as shown in a formula (I),imide resin has a structure in which imide groups superior in thermalcharacteristic and mechanical strength bonded with aromatic groups.Further, the imide resin has a plurality of ether linkages indicatingappropriate melting characteristic upon application of energy such asheat. The thermoplastic polyimide resin having two ether linkages in arepeating unit is preferable because it satisfies required mechanicalcharacteristic, rigidity, heat-resistant property, andinjection-moldability.

(in the formula(I), X is none, namely two phenyl groups bonded directly,or a group selected from hydrocarbon group having 1-10 carbon atoms,isopropylidene group, carbonyl group, thio group, and sulfone group;R₁-R₄ is hydrogen, lower alkyl group (preferably, 1-5 carbon atoms),lower alkoxy group (preferably, 1-5 carbon atoms), chlorine or bromine(R₁-R₄ may consist of the same group or different groups); Y indicatestetravalent group selected from aliphatic group, cyclic aliphatic group,monocyclic aromatic group, condensed polycyclic aromatic group,polycyclic aromatic group in which aromatic groups are bonded to eachother directly or through cross-linking group.)

As such thermoplastic polyimide resin, it is possible to use a productin the trade name of AURUM of Mitsuitoatsu Kagaku Co., Ltd. in which theR₁-R₄ of formula (I) consists of hydrogen.

The polyetherketone resin has a repeating unit shown by a formula (II)shown below or has both the repeating unit of the formula (II)and arepeating unit shown by a formula (III) shown below to such an extentthat the characteristic of the polyether ketone resin is not lost.

As commercially available products of the polyetherketone resin,PEEK150P (VICTREX Inc., trade name), PEK220G (ICI Inc., trade name), andUltrapekA2000 (BASF Inc., trade name) can be used.

It is possible to add, to the resinous composition composing theresinous part 3, solid lubricant such as tetrafluoroethylene resin,graphite, molybdenum disulfide, tungsten disulfide, graphite fluoride,boron nitride, and silicon nitride; a reinforcing material such as glassfiber, carbon fiber, and whisker; and a filler such as calciumcarbonate, clay, and mica.

In the injection molding method of the present invention, the slidingkey is obtained by injecting the resinous composition into a diecontaining the metal-molded part 2. Depending on the configuration ofthe metal-molded part 2, it is possible to adopt one-point gate methodor multi-point gate method. For example, for the sliding key shown inFIGS. 1A and 1B, it is preferable to use two-point gate method. Integralmolding of the sliding key shown in FIGS. 2A and 2B can be accomplishedby one-point gate method.

The continuously variable transmission of the present invention ischaracterized in that it has the above sliding key. The use state of thesliding key is shown in FIGS. 3A and 3B. FIGS. 3A and 3B show the rotaryshaft into which the sliding key is fitted. FIG. 3A is a perspectiveview showing the stepped portion 4 a of the rotary shaft. FIG. 3B is asectional view showing the rotary shaft into which the sliding key isfitted.

In FIG. 3A, the groove 4 b is formed concavely into the periphery of thestepped portion 4 a formed on the periphery of the rotary shaft suchthat the groove 4 b is long in the longitudinal direction of the steppedportion 4 a. The groove 4 b is formed on the stepped portion 4 a at oneposition thereof or preferably, at several positions thereof at regularintervals in the circumferential direction thereof. The sliding key 1 isfitted into the groove 4 b and engages the sliding cylindrical portion(FIG. 3B).

In the continuously variable transmission of the present invention, eachof other constituent elements thereof may have the same construction asthat of the conventional one shown in FIG. 4, except the sliding key.Example 1 through example 4 and comparison examples 1 and 2.

As the resinous composition, a thermoplastic polyimide resinouscomposition (Bearee PI5010: trade name made of NTN engineering plasticsCorporation) and a polyetherketone resinous composition (Bearee PK5900:trade name made of NTN engineering plastics Corporation) were prepared.As the metal-molded part, surface-plated machine parts havingconfigurations same as those shown in FIGS. 1A and 2A were prepared.

The metal-molded part was placed in the cavity of the die and injectionmolding was performed in an injection molding condition (thermoplasticpolyimide resinous composition: pressure; 255 Mpa, temperature; 410° C.,polyetherketone resinous composition: pressure; 255 Mpa, temperature;380° C.). As a result, a sliding key that was a composite integralmolded product of the metal-molded part and the resinous part and havingthe configuration shown in FIGS. 1A and 2A was obtained.

As shown in FIGS. 3A and 3B, to fit the sliding key having the resinouspart into the corner-rounded groove 4 b formed on the stepped portion 4a, both ends of the sliding key in the axial direction thereof weremachined into the same configuration as that of the groove 4 b toprevent the sliding key from dislocating against a load allied theretoin the axial direction of the rotary shaft.

The obtained sliding key was evaluated in a repeating shearing fatiguetest and a friction test for measuring its friction coefficient. Therepeating shearing fatigue test (FIG. 6) and the friction test (FIG. 7)were conducted in accordance with the NTN method. The evaluated resultis shown in table 1. The result of comparison examples 1 and 2 wasobtained by evaluating sliding keys formed by using the same method asthat of example 1. However, to form the sliding keys, the thermoplasticpolyimide resinous composition alone and the polyetherketone resinouscomposition alone were used respectively.

TABLE 1 repeating friction test shearing (friction fatigue testcoefficient) sliding key load torque, face pressure, configuration resin50N · m 47Mpa Example 1 FIG. 1 PI not less 0.05-0.08 than 200,000Example 2 PEEK not less 0.2-0.3 than 300,000 Example 3 FIG. 2 PI notless 0.05-0.08 than 150,000 Example 4 PEEK not less 0.2-0.3 than 225,000comparison — PI not more 0.05-0.08 1 than 50,000 comparison PEEK notmore 0.2-0.3 2 than 75,000 note) PI:thermoplastic polyimide resinouscomposition PEEK: polyether ketone resinous composition

As shown in table 1, the sliding key of example 1 through example 4indicated repeating shearing fatigue characteristic values more thanthree times as great as that of the sliding keys made of the singleresinous composition, respectively and indicated friction coefficientsequal to those of the sliding keys made of the single resinouscomposition, respectively.

A continuously variable transmission as shown in FIG. 4 was assembledfrom the sliding key of example 1 and example 3. As a result, thecontinuously variable transmission did not have seizing and was notdestroyed when they were used in an environment where temperature wasabout 110° C., load was 250 kgf, and sliding speed was 1.3 mm/sec.

INDUSTRIAL APPLICABILITY

The sliding key of the present invention is a composite integral moldedproduct of the metal-molded part and the resinous part. Thus, when thesliding key is used in an environment of a high temperature and a highload, it does not have seizing or is not destroyed.

Further, because the resinous part is made of the injection-moldableresinous composition, it is easy to mold the resinous part integrallywith the metal-molded part having a complicated configuration to formthe composite integral molded product. Consequently, it is possible toobtain the sliding key superior in mechanical characteristic and low incost.

Because the continuously variable transmission of the present inventionuses the above-described sliding key, it is allowed to have a simpleconstruction. Therefore, it is possible to obtain the continuouslyvariable transmission compact, lightweight, and inexpensive.

What is claimed is:
 1. A sliding key engaging a sliding cylinder withsliding in an axial direction and following a rotation of a rotary shaftcomprising a composite molded product, said product is made of ametal-molded part and a resinous part.
 2. A sliding key according toclaim 1, wherein said resinous part consists of an injection-moldableresinous composition.
 3. A continuously variable transmissioncomprising: a stationary pulley rotating with a rotary shaft having aplurality of grooves formed on a peripheral surface thereof atappropriate intervals in a circumferential direction thereof and havinga sliding key fitted into each of said grooves; and a movable pulleyhaving a sliding cylinder having a plurality of grooves each of whichhas a width to receive said sliding key and extends axially on an innerperipheral surface thereof such that said grooves are located atappropriate intervals in correspondence to said grooves formed on saidperipheral surface of said rotary shaft, wherein said sliding key is thesliding key of claim 1.